This research seeks to determine the neural mechanisms that mediate cellular dehydration thirst. In acute experiments, multiple unit and unit responses are recorded from different brain areas during hypertonic challenges, in order to determine which brain structures contain osmosensitive neurons. Autonomic responses of these structures to hypertonic challenge and to electrical stimulation are also being investigated. In chronic experiments, the effects of waking activities on hyperosmotically challenged neural activity in these brain structures are being investigated. BIBLIOGRAPHIC REFERENCES: Malmo, R.B. Osmosensitive neurons in the rat's dorsal midbrain. Brain Research, 1976, 105, 105-120. Malmo, R.B. Guarding against "subcortical phrenology." (Review of Limbic and autonomic systems research by L.V. DiCara (Ed.)). Contemporary Psychology, 1976, 21, 26-27.